Recently mandated vapor emission requirements for motor vehicle fuel tank systems have required that the system seal about the dispensing nozzle to prevent escape of fuel vapor to the atmosphere during refueling and such systems are often referred to as On-Board Refueling Vapor Recovery (ORVR) Systems. When a seal is disposed about the refueling nozzle, it is necessary to recirculate fuel vapor to the upper end of the filler tube in the region surrounding the nozzle in order to prevent the aspiration effect of nozzle discharge from causing premature activation of the vacuum sensitive automotive shutoff mechanism provided in the dispensing nozzle.
In current production motor vehicles, the more widely used systems rely upon the rising fuel level in the tank to cover the end of the vapor recirculation tube connected to the tank to thereby shut off the flow of recirculating vapor and create a vacuum in the region of the filler tube about the dispensing nozzle and thus activate the automatic shutoff mechanism in the dispensing nozzle.
However, problems have been encountered in service where the seal about the dispensing nozzle leaks. In this event, the rising fuel in the tank closes the recirculation tube; however, the air leakage about the nozzle seal provides sufficient make-up air for the aspiration effect of the fuel discharging from the nozzle so as to prevent the formation of a vacuum and thus failure of the automatic nozzle shutoff occurs.
Thus, it has been desired to provide a simple, low cost yet effective way of insuring appropriate shutoff of a fuel dispensing nozzle in a tank filler tube and to prevent failure of the nozzle shutoff due to improper sealing about the nozzle and to prevent fuel from backing up in the filler tube and spilling to the atmosphere.